This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Bacteria cope with life in harsh environments using specific stress responses and chemical alterations of cell components. We explore the biochemical strategies for survival at low pH employed by a naturally acid-resistant bacterium, Acetobacter aceti, which has the ability to handle low pH in general -- its cytoplasmic pH can drop as low as 4 -- and acetic acid in particular. This Gram-negative, plant-associated bacterium has been used for millenia in the production of vinegar. Acetic acid is especially toxic to bacteria at low pH because it forms dimers that easily permeate cell membranes. Kappock's approach to this problem is centered on enzyme function at low pH, assisted by several in-progress genome sequencing projects. We found that individual A. aceti enzymes retain function in acid much longer than comparable forms from non-acidophilic organisms. X-ray crystallography has revealed distinctive architectural features of A. aceti proteins that may confer this stability. We have also delineated metabolic strategies for acetic acid elimination by highly-resistant strains, which may be employed by other microbes including several pathogens.